1. Field of the Invention
This invention relates principally to an electromagnetic radiation measuring apparatus and its electromagnetic radiation measuring method for measuring the strength of radiation emanating from electronic equipment, and more particularly, to an electromagnetic radiation measuring apparatus and its electromagnetic radiation measuring method suited for measuring an electromagnetic radiation of over 1 GHz.
2. Description of Related Art
Since electromagnetic noise generating in various kinds of electronic equipment and systems may sometimes emit to free space to cause interference with the functions of other equipment, recent years have seen increasing levels of attention paid for electromagnetic dichotomy through suppression of such electromagnetic radiation (or radiated emission) and improvement of interference elimination capability, that is, EMC (Electro-Magnetic Compatibility). As methods of measuring such electromagnetic radiation, the following are known on the basis of the measuring standards of ANSI (American National Standards Institute).
An example of a conventional method for measuring electromagnetic radiations is shown schematically in FIGS. 11A and 1113. FIG. 11A illustrates a method for spiral-shaped sampling, while FIG. 11B shows a method for round sliced sampling.
This measuring method is typically conducted in a anechoic chamber, and the equipment under test (hereafter referred to as the xe2x80x9cEUTxe2x80x9d) 102 is placed on a turntable 105, which is revolved through 360 deg at a rate of over 5 rpm, an antenna 103 receiving while being moved up in the perpendicular direction at a height ranging from 1 m to 4 m, the measurement being conducted by obtaining a maximum field intensity of the electromagnetic radiation. This measuring can be considered virtually equal to the condition wherein a surface of a cylindrical plane 105a with the turntable 105 in the center is being scanned by the antenna 103, as schematically shown in FIGS. 11A and 11B. For example, when the antenna 103 is moved in the perpendicular direction while turning around the turntable 105, continuous sampling is performed in the spiral shape as illustrated in FIG. 11A, while in the case of holding the height of the antenna 103 at a fixed interval, sampling is conducted in the manner of cutting in round slices per fixed height as illustrated in FIG. 11B. Now, when a maximum value measured in such measuring exceeds the specified value, a decision of xe2x80x9cInappropriatexe2x80x9d is given.
It should be mentioned that insofar as electromagnetic radiations of more than 1 GHz are concerned, as a result of effects of reflected waves from a metallic ground plane comprising the bottom of the anechoic chamber, the electromagnetic waves draw very fine height patterns. An example of the height pattern due to a horizontal polarization of 3 GHz is illustrated in FIG. 12, and an example of the height pattern due to a horizontal polarization of 5 GHz is shown in FIG. 13.
As shown in FIG. 12 and FIG. 13, since the peaks of the electric field values appear minutely with respect to the perpendicular direction in these electromagnetic radiations, in the case of a measuring method of obtaining the maximum radiation level per frequency by rotating the aforementioned turntable 105 at a high speed of more than 5 rpm, there is an extremely good possibility that the maximum peak is overlooked, which results in an inaccurate measurement.
This point is taken into consideration by ANSI which describes the following measuring method for measuring the electromagnetic radiation of over 1 GHz as an empirical technique, urging that due caution be exercised in the measurement thereof. For instance, after a horn antenna is moved close to the vicinity of the EUT, ascertaining the direction of intense noise radiation, measurements are made with respect to the range thereof by changing the antenna""s position per specified height.
Yet, a fact remains that this conventional measuring method calls for a great deal of time determining the range of strong noise radiation and searching for angles. For example, this measurement generally takes over 40 minutes by an operator well experienced in this measurement and more than an hour by a designer of the EUT 102, thus requiring a plurality of operators to shorten the time. There is an additional disadvantage in that the beam characteristic is sharp in the height direction, which very likely results in that the designer with no measuring skills would overlook the peak value without performing accurate measurements.
The present invention is directed to resolving the foregoing problems inherent in the conventional technique. It is therefore an object of the present invention to provide an electromagnetic radiation measuring apparatus which can measure an electromagnetic radiation of more than 1 GHz accurately and in a short time.
It is another object of the present invention to provide a method for measuring the electromagnetic radiation which can measure an electromagnetic radiation of more than 1 GHz accurately and in a short time.
According to the present invention, there is provided an electromagnetic radiation measuring apparatus for measuring electromagnetic radiations from electronic equipment including: detection means for detecting the electromagnetic radiation; perpendicular drive means for driving the detection means in a perpendicular direction; rotary drive means for driving the electronic equipment revolvingly; field intensity measuring means for measuring a field intensity of each frequency from a detection signal of the detection means; data analysis means for analyzing measured data of the field intensity and for outputting a maximum field intensity of each frequency with respect to all measured data or a direction characteristic of the field intensity at the preceding frequency; and measurement control means for exerting control for revolving and stopping the rotary drive means per specified angle, moving the detection means within a range of a specified height by the perpendicular drive means upon suspension of revolution, causing the field intensity measuring means to receive the detection signal continuously during the movement of the receiving means, calculating the frequency spectrum based on the maximum field intensity of each frequency per suspension of revolution, and causing the data analysis means to receive the frequency spectrum due to be subsequently subjected to analysis.
In the electromagnetic radiation measuring apparatus of this arrangement, the measuring control means operates so that the electronic equipment is revolved per specified angle by the rotary drive means, the detection means being moved by the perpendicular drive means in the perpendicular direction per suspension of revolution so as to continuously detect electromagnetic radiations, the frequency spectrum based on the maximum of each frequency being automatically measured by the field intensity measuring means, wherefore the electromagnetic radiation measurement can be performed with high accuracy and in a short time without overlooking the point wherein the radiate emission reaches its maximum.
Moreover, according to the electromagnetic radiation measuring method of the present invention for measuring electromagnetic radiations from the electronic equipment, there is provided a method of measuring electromagnetic radiations which moves revolvingly the electronic equipment mentioned above per specified angle, detects the electromagnetic radiations continuously in the perpendicular direction within the range of a specified height upon suspension of revolution, calculates the frequency spectrum which recorded the maximum field intensity of each frequency per suspension of revolution, analyzes the maximum field intensity of each frequency with respect to all measured data as well as the direction characteristic of the field intensity at each frequency described above, and outputs such results.
In the above-mentioned electromagnetic radiation measuring method, since the electronic equipment is revolved per specified angle, electromagnetic radiations are detected continuously in the perpendicular direction within the range of the specified height per suspension of revolution, the frequency spectrum based on the maximum field intensity of each frequency being measured automatically. Therefore, there is no overlooking the point wherein the electromagnetic radiation reaches its maximum, and the electromagnetic radiation measurement can be performed with high accuracy and in a short time.
As the described above, the embodiment of the present invention is shown by illustrating an electromagnetic radiation measuring apparatus, in which by dint of the control exerted by the measuring control means, the rotary drive means revolves the electronic equipment per specified angle, the perpendicular drive means moving the detection means in the perpendicular direction per suspension of revolution for continuous detection of electromagnetic radiations, the field intensity measuring means automatically measuring the frequency spectrum based on the maximum of each frequency, so that the point where the electromagnetic radiation becomes a maximum is not overlooked, enabling electromagnetic radiations to be measured with high accuracy and in a short time.
Also, the embodiment of the present invention is shown by illustrating an electromagnetic radiation measuring method, since the electronic equipment is revolved per specified angle, electromagnetic radiation is detected continuously per suspension of revolution in the perpendicular direction in the range of the specified height, and the frequency spectrum based on the maximum of each frequency is automatically measured, the point where the electronic radiation becomes a maximum is not overlooked, enabling electromagnetic radiations to be measured with high accuracy and in a short time.